1. Field of the Invention
This invention relates to a stencil plate.
2. Description of the Related Art
Heat sensitive stencil paper sheets which can be perforated by irradiation of infrared rays or by means of a thermal head are conventionally known. A typical one of the conventional heat sensitive stencil paper sheets includes a heat sensitive film and a porous thin paper sheet adhered to the heat sensitive film using a bonding agent. A stencil paper printing apparatus using a single cylinder, such as shown in FIG. 8, is known for using this described conventional heat sensitive stencil paper sheet. Referring to FIG. 8, the stencil paper printing apparatus includes a plate cylinder 62 which has a perforated photosensitive stencil paper sheet 64 wound on an outer periphery thereof with its porous support member positioned on the inner side. Ink is supplied from the inside toward the outer periphery of the plate cylinder 62. A press roller 66 is contacted under pressure with the plate cylinder 62 with printing paper 68 interposed therebetween while the plate cylinder 62 is driven to rotate to effect printing on the printing paper 68.
Shown in FIG. 9 is a second type of conventional stencil paper printing apparatus. Referring to FIG. 9, the stencil paper printing apparatus uses a heat sensitive stencil paper sheet 70 formed of a heat sensitive film. A porous support member 84 is adhered to the heat sensitive film and has a frame member 72 provided along a periphery of the porous support member 84. The porous support member 84 serves as an ink applying portion and is enclosed by the frame member 72 and an ink-impermeable cover sheet 74.
The stencil paper printing apparatus includes a pressing member 78, a receiving table 80 disposed in an opposing relationship to the pressing member 78, and a holding member 82 disposed at a peripheral portion of the face of the pressing member 78, opposed to the receiving table 80, for holding the heat sensitive stencil paper sheet 70 thereon. Ink is applied to the porous support member 84, surrounded by the frame member 72, of the perforated heat sensitive stencil paper sheet 70. Then the porous support member 84 and the frame member 72, attached on one side to heat sensitive stencil paper sheet 70, are covered with the cover sheet 74 on the opposite side prior to mounting on the pressing member 78. The heat sensitive stencil paper sheet 70 is held on the pressing member 78 by the holding member 82 and the pressing member 78 is moved toward, and pressed against, the receiving table 80 with printing paper 86 interposed therebetween to effect printing on the printing paper 86.
A stencil paper printing apparatus of the cylinder type described above has a large size. Since it can be used to print large stencils, it has a comparatively high running cost when required to print comparatively small amounts of material, i.e. only a small portion of the stencil has printing perforations.
On the other hand, the pressing type stencil paper printing apparatus has a comparatively small size. However, it has a disadvantage in that the user must apply the ink. Therefore, the hands or the clothes of the user may be soiled when the ink is applied and, since the ink is not readily applied with a uniform thickness, a regular print may not be obtained.
In order to improve the drawbacks of the conventional stencil paper printing apparatuses described above, the applicant of the present invention described, in Unexamined Japanese Patent Provisional Publication No. 4-166390 (published Jun. 12, 1992), a plate for stencil paper printing as shown in FIG. 10.
Referring to FIG. 10, the stencil plate 50 includes successive layers of a heat sensitive stencil paper sheet 56 formed of a thermoplastic film 52 and a porous support member 54 adhered to the thermoplastic film 52, a non-woven fabric 58 disposed on the heat sensitive stencil paper sheet 56 adjacent to the porous support member 54 and impregnated with ink, and an ink-impermeable film 59 serving as a base member. A perforation image is formed on the stencil plate 50 by heat melting the thermoplastic film 52 of the heat sensitive stencil paper sheet 56 by means of a stenciling apparatus which employs, for example, a thermal head. Such formation of a perforation image will be hereinafter referred to as stenciling.
The stencil plate 50, thus stenciled, is mounted onto a stamping member provided with a grip and the stamping member is pressed against printing paper to effect stencil paper printing.
However, with the stencil plate, when it is stenciled, for example, by means of a thermal head, a small amount of ink oozes from the perforation portions and, accordingly, there is the possibility that ink may stick to the thermal head and also to the face (printing face) of the thermoplastic film of the stencil plate.
A stencil plate which solves the above identified problem has been developed and is shown in FIG. 11. Referring to FIG. 11, the stencil plate 10 includes, as principal components thereof, a heat sensitive stencil paper sheet 12, a separator 14, a non-woven fabric 16 impregnated with ink, a frame member 18 disposed so as to surround the non-woven fabric 16, and an ink-impermeable film 20 serving as a base member.
The heat sensitive stencil paper sheet 12 includes, as shown in FIG. 13, a thermoplastic film 22, a bonding agent layer 24, and a porous support member 26. The thermoplastic film 22 is formed of a polyethylene terephthalate film (hereinafter referred to as PET film) approximately 2 .mu.m thick, but may alternatively be formed of a film of, for example, polypropylene or copolymer of vinylidene chloride-vinyl chloride. Preferably the PET film is 1 to 4 .mu.m thick. A thickness, of the PET film, of less than 1 .mu.m results in high production costs and does not provide sufficient strength. Accordingly, the PET film of such thickness is not suitable for practical use. The porous support member 26 is formed of thin porous paper which is made of, as a principal material, for example, natural fiber of Manila hemp, kozo (paper mulberry =Broussonetia kazinoki) or mitsumata (Edgeworthia papyrifera), synthetic fiber of polyethylene terephthalate, polyvinyl alcohol or polyacrylonitrile or semisynthetic fiber of rayon. The heat sensitive stencil paper sheet 12 structured as described above adheres, at four sides thereof, to the frame member 18 by means of a bonding agent layer 28 as shown in FIG. 12.
An opening 17 having a size corresponding to the size of the non-woven fabric 16 is formed at a central portion of the frame member 18 as shown in FIGS. 11 and 12. A small hole 19 for removing the separator 14 therethrough is formed at a right portion of the frame member 18 (as shown in FIGS. 11 and 12). Since the ink impregnated in the non-woven fabric 16 is an oil ink, the frame member 18 is made of a material which is not attacked by oil ink, such as, for example, vinyl chloride, polypropylene, polyethylene, polyacetal or polyethylene terephthalate.
The non-woven fabric 16 is impregnated, in a saturated condition, with the oil ink so that when a pressure is applied to it, the ink impregnated therein oozes from the non-woven fabric 16. The non-woven fabric 16 is made of a synthetic fiber of polyethylene, polypropylene or polyethylene terephthalate. Preferably the thickness of the non-woven fabric 16 is set greater than one half but smaller than three times the thickness of the frame member 18. Upon stenciling, while the heat sensitive stencil paper sheet 12 is moved by transporting the frame member 18, it is perforated by heat of a thermal head. Accordingly, if the thickness of the non-woven fabric 16 is excessively small, the heat sensitive stencil paper sheet 12 will sink into, upon stenciling, the inside of the frame member 18 and be moved out of contact with the thermal head thereby resulting in a failure to achieve complete perforation. On the other hand, if the thickness of the non-woven fabric 16 is excessively great, then it projects from the frame member 18 to be compressed against the thermal head. In this condition, the stencil plate 10 is prevented or hindered from being transported regularly by the frame member 18 during stenciling. Accordingly, because the stencil plate 10 is not transported properly in the predetermined pitch, or is transported obliquely due to the non-uniform thickness of the non-woven fabric 16, the perforations are improperly positioned. Preferably, the non-woven fabric 16 is set so that it is compressed, upon stenciling, by the pressing force of the thermal head so that it presents a thickness equal to that of the frame member 18.
The separator 14 is disposed between the heat sensitive stencil paper sheet 12 and the non-woven fabric 16. A portion thereof, shown in FIG. 12 as a right portion, extends through the small, oblong hole 19 formed in the frame member 18 and further between the frame member 18 and the film 20 to project beyond the end of the stencil plate 10.
The size of the separator 14 is set to be greater than the size of the non-woven fabric 16. More particularly, referring to FIG. 12, the area the separator 14 covers beyond the non-woven fabric 16 is defined by a chain line shown on the frame member 18. The separator 14 may be formed of mold separating paper produced by applying a silicon film to wood-free or glassine paper or of a resin film of polyethylene terephthalate or ethylene tetrafluoride (trade name: TEFLON). The material of the separator 14 is required to have the characteristic that it is low in wettability and, more particularly, the wetting angle is 45 degrees or more. Further, when mold separating paper or the like is employed, preferably a silicon film is formed not only on the face of the mold separating paper contacting the non-woven fabric 16 but also on the other face as well. When the wettability is high, or a silicon film is formed on only one face of the mold separating paper or the like, the ink may spread to the heat sensitive stencil paper sheet 12 side of the separator 14 and there is the possibility that, when perforations are formed, ink may ooze from the perforation portions.
The ink impermeable film 20, which serves as a base member, has a bonding agent layer 32 applied to an upper face (slanting line portion in FIG. 12) for adherence to the frame member 18 and the non-woven fabric 16. The film 20 is formed of a film of a resin which is not attacked by oil ink such as vinyl chloride, polypropylene, polyethylene or polyethylene terephthalate.
The stencil plate 10 described above is stenciled using a stenciling apparatus (not shown). Such a stenciling apparatus mirror-image prints the face of the thermoplastic film 22 of the heat sensitive stencil paper sheet 12 by means of a thermal head to heat the thermoplastic film 22 to melt and perforate same. When stenciling, the thermal head is pressed against the stencil plate 10 under a predetermined pressing force and, in this instance, since the separator 14 is disposed between the heat sensitive stencil paper sheet 12 and the non-woven fabric 16, even if the thermoplastic film 22 of the heat sensitive stencil paper sheet 12 is perforated, ink does not ooze from the perforation portions.
The stencil plate 10, stenciled in this manner, is mounted onto a stamping member 34 (shown in FIG. 14). The stamping member 34 consists of a handle portion 36, a cushion layer 38 and an adhesive layer 40. The stencil plate 10 is mounted onto the stamping member 34 by adhering the film 20 side of the stencil plate 10 to the adhesive layer 40 of the stamping member 34. Thereafter, the separator 14 (shown in FIG. 12) is pulled from the stencil plate 10. The stamping member 34 can then be pressed against a printing paper 42, whereupon the non-woven fabric 16 is compressed so that ink oozes from the perforated portions of the printing face of the stencil plate 10 and is transferred to the printing paper 42.
The conventional stencil plate 10, however, has several problems, such as the formation of irregular perforations caused by slippage between the separator 14, having a low wettability, and the heat sensitive stencil paper sheet 12 upon formation of an image on the heat sensitive stencil paper sheet 12, soiling of the thermal head of the perforating stenciling apparatus caused by ink oozing from an end face of the separator 14 to the heat sensitive stencil paper sheet 12 side, and the production of wrinkles in the heat sensitive stencil paper sheet 12 upon stamping caused by the admission of air between the non-woven fabric 16 and the heat sensitive stencil paper sheet 12 upon removal of the separator 14 after formation of an image.